After the Lord of the Rings trilogy, Viggo Mortensen could have been a movie star who slides across car hoods while shooting an automatic pistol or, alternately, who arrives just in time to sooth Drew Barrymore's broken heart. Instead, the actor-painter-poet has used the credit he earned to take chances, most successfully with David Cronenberg's acclaimed History of Violence. Mortensen says he was honored to be asked to reteam with Cronenberg, whom he calls "one of the true visionaries in contemporary film," on Eastern Promises, which opens Friday. The drama, which took the audience prize at the just-ended Toronto International Film Festival, stars Mortensen as Nikolai, a Russian expatriate ostensibly working as a driver for a Russian mobster (Armin Mueller-Stahl) in London. His real job, however, is looking after the mobster's volatile but vicious son (Vincent Cassel). A birth and a death - both symbolically bloody, this being Cronenberg - bring Nikolai together with a midwife (Naomi Watts) who had a Russian father but is otherwise unconnected to her roots. Mortensen did his usual role preparation - immersing himself in Russian history and poetry and spending time in St. Petersburg, Moscow and the Ural Mountains.

He studied the language, he says, with a Russian professor, then learned it all over again to incorporate the slang and speaking style common to a Russian who has spent time in prison. He learned the real history of his character, he says, from his tattooed-covered body.

"It's the language of prison culture," says Mortensen. "In Russia, your tattoos explain where you've been and why. The gangs are called 'thieves in law,' and they all have distinctive markings. It's fascinating stuff, very tribal."

Cronenberg had been working on another project when he was sent Steven Knight's screenplay for Eastern Promises. Knight had explored the world of immigrants in London in the Stephen Frears-directed Dirty Pretty Things, and Cronenberg says he had always been intrigued by the way people adapt or don't adapt to foreign culture.

"Toronto was multicultural before the word was coined," says the Canadian director. "The influx of immigrants was gradual, and while I'm sure there were many people threatened and disturbed by it, there were just as many who welcomed all the new ideas and contributions, and having a university right downtown probably made the integration easier, too. But the fact is that every culture sort of creates its own reality in places like Toronto or London.

"In the States, I think you're more wedded to this idea of the melting pot, where everyone is supposed to assimilate and bring forth this new thing, become new Americans. But they still bring the old country with them, and as Naomi learns in the movie, it's always there, even if you've ignored it. It comes back whether you look for it or not. It looks for you."

Cronenberg says the original script was naturally changed by his own preoccupations. "To me, all my movies are the same, from the early horror films to this one. I'm still exploring the same ideas of identity and duality that I was in Dead Ringers or M. Butterfly. When people say this film or that film is a departure, I don't know what to say. People have said this is more of a straight genre film, but I can't view it like that. It's just a different way into the same maze of human contradiction."

Cronenberg says Promises is definitely more of a collaboration than most of his other films because of Mortensen.

"There was actually very little made of the tattoos in Steven Knight's script. Viggo brought that in by discovering this book about Russian prison tattoos and through this documentary, a friend of his made, The Mark of Cain, that explains how this has been part of the culture since the czarist era. I learned in the last film that you don't make a movie with Viggo in it; you make a movie with Viggo. He doesn't try to impose himself the way some actors do. He just assumes we're all in it together to make the most emotionally and dramatically accurate representation of life that we can."

It was that commitment, says Cronenberg, that begat the most controversial sequence in the film, a violent, extended bathhouse assault that Mortensen plays nude.

"David asked me how I wanted to shoot it, and I told him I didn't think there was any other way to do it. If I had somehow managed to keep a towel on in that struggle to the death, or if we had shot it behind columns or used tricky camera angles or something that concealed the body, audiences would have seen through that, it would have been avoiding the truth of that violence, and then it would have been phoney, just another fight scene. I may not be comfortable being naked before a camera, but I would have been less comfortable doing something false. It's just the way I'm made."